Continuous casting apparatus including endless steel belt with red iron oxide coating



J ly 1955 s. H. ROCHESTER 3,193,888

CONTINUOUS CASTING APPARATUS INCLUDING ENDLESS STEEL BELT WITH RED IRON OXIDE COATING Filed Aug. 29, 1961 TENSION ROLL METALLIC BELT MOLTEN 6mm: METAL 21 ROLL i H POWER Z2 ROLL To SIZING ROLLS 2 Q 20 3 1 a e TENSlON was 24 RoLL GROLL 24 a souv METAL SLAB 25 SHEET 0R FILM METALLIC BELT 15 J POWER ROLL Tn E.

. Raven, ADHERENT 31 lRON oxws COATING \I r T 6 STEEL eEL INVENTOR. Lim/vm H flaw/Esme imam United States Patent 0 3,193,888 CONTINUQUS CASTHNG APPARATUS INCLUDING ENDLESS STEEL BELT Wi'llll RED RGN OXIDE (IGATENG Stanley Herbert Rochester, Kingston, Ontario, Canada, assignor to Aluminium Laboratories Limited, Montreal, Quebec, Canada, a corporation of Canada Filed Aug. 29, 1961, Ser. No. 134,695 1 Claim. (Cl. 22S7.4)

This invention relates to the casting of metals. More particularly, this invention relates to a continuous metal casting operation and apparatus useful therein. Still more particularly, this invention relates to a continuous metal casting operation wherein molten metal is poured or continuously introduced between two continuously and synchronously moving, endless belts, the opposed adjacent surfaces of the metal belts between which the molten metal is introduced serving as a mold for the solidification of the molten metal.

In the so-called Hazelett continuous metal strip casting process and apparatus for the casting of aluminum, aluminum alloys and the like, molten metal, such as molten aluminum, is introduced at one end of the casting machine between two continuously and synchronously moving, fiat metal, usually mild steel, strips or belts. The belts, generally horizontal, but traveling downward together at a small angle, are vertically spaced to define the desired thickness of the strip or slab to be produced, and are cooled during the casting operation by large flows of water. As the molten metal is introduced between the belts and held by moving dams at the sides, it is cooled and at least partially solidified by contact with the belts while being carried on the moving belt upon which the metal is deposited so that with suitable control or setting of the distance between the opposed surfaces of the moving belts a solid cast metal strip of substantially uniform dimensions and substantially free of surface defects is produced and removed from the other end of the casting machine. Certain forms of belt casting apparatus are shown in US. Patents Nos. 2,640,- 235 and 2,904,860, issued to C. W. Hazelett on lune 2, 1953 and September 22, 1959, respectively, but Hazelett machines now in use embody further improvements, in cooling and otherwise, and are arranged, as in the second cited patent, to keep the endless belts flat throughout their travel in the casting section of the machine.

During the above-described continuous metal casting operation the endless metal belts must be, and run, flat during the casting and solidification process. Further, the metal belts must provide the correct degree of resistance to heat transfer which, in turn, varies with the metal being cast. It is desirable in such a continuous metal casting operation to protect the metal surfaces of the belts in contact with the molten metal against unduly high temperatures to prevent distortion of the belts due to thermal expansion. Further, since the metal belts are run under tension and are flexed as they pass over pulleys, any insulative, protective material or dressing employed thereon must not only be temperature resistant, i.e. refractory, but must be flexible, and adherent to the metal surface of the belt to which it is applied.

In the past it has been the practice to coat the surfaces of the belts in contact with the molten metal with an organic resin, such as polyvinyl butyral resin containing a metal chromate, e.g. zinc chromate, dispersed therein. It has also been proposed to provide these metal belts with an insulative, refractory coating of diatomaceous earth and the like.

For the most part, however, these coating materials have not proved to be completely satisfactory particularly since they do not possess the high temperature properties and the degree of thermal stability which will enable them to withstand for a long period of time the impingement of molten metal, such as molten aluminum.

Accordingly, it is an object of this invention to pro vide an improved, temperature resistant, insulative coating on metal surfaces, such as on the outside surfaces of endless metal belts employed in a metal casting operation.

It is another object of this invention to provide an improved Hazelett metal strip casting operation and machine therefor.

Another object of this invention is to provide an improved continuous metal casting operation for the continous casting of metal strip and the like.

Still another object of this invention is to provide an endless metal belt having a temperature resistant, refractory coating thereon.

How these and other objects of this invention are achieved will become apparent in the light of the accompanying disclosure made with reference to the accompanying drawings wherein:

FIG. 1 schematically illustrates the Hazelett continuous metal strip casting process and machine therefor; and

FIG. 2 is a schematic, cross-sectional view of a continuous metal belt coated with a composition in accordance with this invention.

It has now been discovered that a coating of a rough or pitted, adherent iron oxide provides an excellent, temperature resistant, insulative coating for the surfaces of metal belts employed in a metal casting operation. Still more particularly, it has now been found that an adherent, rough iron oxide coating formed on the outside surface of an endless steel belt, such as an endless, mild steel belt employed in the Hazelett continuous metal strip casting process, protects the coated metal surface against high temperature and against the impingement of molten metal, such as molten aluminum or molten aluminum alloy. As a result of the operation whereby the adherent iron oxide is formed on the steel surface, the surface, originally smooth, becomes pitted and roughened as the iron oxide formation progresses due to the oxidation of the underlying steel surface.

Any suitable method may be employed to form the rough, flexible adherent iron oxide coating on the steel surface to be protected. it is preferred in the practice of this invention to form an adherent, flexible rough iron oxide coating on the outside surface of a steel belt in the following manner. There is applied to the outside surface of an endless, mild steel belt, such as a belt having a thickness in the range 0.030.3", more or less, an aqueous solution of mineral acid, such as a 10% aqueous solution of hydrochloric acid, in order to promote rusting of the surface to which the acid is applied. The thus-treated surface is then permitted to dry. The other side or surface, the inner surface of the mild steel belt has provided thereon a protective coating such as by applying a film or coating of oil, paint, lacquer or suitable grease, asphaltic or bituminous coating thereon. The thus-treated and coated belt is then exposed to contact with an atmosphere containing gaseous oxygen and water vapor for a period of time and under conditions such that there is formed on the outside, acid-treated surface of the metal belt an adherent iron oxide coating having a suitable roughness, such as a uniform hard, substantially evenly pitted iron oxide coating, the pits thereon being at least about 0.0G2 inch in depth. This adherent iron oxide coating can be readily obtained by exposing the treated metal belt to the weathering effect of outside atmosphere, preferably under damp, relatively high humidity conditions, eg above about 40% humidity, more or less, and at an ambient temperature in the range 30l00 R, more or less. If desired, a controllable, rust-producing environment can be artificially provided within a suitable chamher or enclosure supplied with air or elemental oxygen and within which relatively high humidity conditions, about 90%, and controlled. temperature conditions can be maintained. By employing such a controlled, rust-producing environment, the rate of formation of the desired iron oxide coating can be greatly increased. For example, it has been found that when outside weathering is employed at least a month exposure to theoutside atmosphere is usually required before a satisfactory 'iron oxide coating havprotected against contact with the hot molten metal by ing an evenly pitted surface with a pit depth of at least 7 0.002 inch is formed. n the other hand, by utilizing an artificially created, rust-producing environment, i.e. by use of a chamber operated at a relatively high temperature, above about 75 F, ditions, above'about 80% humidity, an adherent iron and under high humidity'conoxide coating having the desired roughness and thickness can be obtained in about 2-4 weeks.

Following the formation of the iron oxide coating on the thus-treated steel bel it is desirable, before the belt is employed in a continuous metal castingoperation, that any loose rust or surface scale be removed from the rustv coated surfac such as by lightly scouring or cleaning the rust-coated surface with steel wool. Also desirably, following the removal of loose rust, the rust-coated surface is provided with a coating of graphite, such as by applying to the rust-coated surface a suspension of graphite in a carrier liquid, e.g. a 50% by weight graphite suspension in isopropanol. Various steel belts such as steel belts made from lightly embossed (culvert stock) steel strip and mild steel belts are thus satisfactorily treated in accordance with this invention.

Referring now to FIG. 1 of the drawing which schematically illustrates the application of thisinvention to the Hazelett continuous metal strip casting process and 'machine, molten metal, such as molten aluminum or molten aluminum alloy, is supplied from a suitable source, not shown, via feed box or spout at one end of the castin machine into the space between continuously moving steel belts 11 and 12. In accordance with this invention the opposed surfaces of belts iii and 12 in contact with the molten metal are provided with an adherennrough iron oxide coating in accordance with this invention. ably, the iron oxide coating has a film of graphite deposited thereon. p

The illustration of the machine in FIG. 1 is purely diagrammatic, it being understood that whereas the arrangement of belt, rolls or pulleys somewhat follows that of the cited patent US. 2,640,235, other arrangements can be and are used as may be desired. As here shown belt ill passes over tension pulley l4 and driving pulley 15 and belt 12 passes over tension pulley ldand driving pulley 18. At the metal feed end, appropriate means, shown as guide rolls i9 and 20, bring the belts together to forma vessel for the metal 21, it being understood that throughout the metal-receiving and casting region the pair of belts is flanked by traveling dams or Walls (not shown) whereby the metal, as it cools, is continuously retained in a rectangular region defining the cross-section of the strip to be produced. I v

. As generally indicated in FIG. 1 belts Hand 12 move continuously and synch onously while cooling water, from means not shown, is flushed across the upper surface of belt 12 and the lower surface of belt. 11, along the region where the metal is carried between them. An appropriate series of rolls, preferably closely spaced, but here indicated simply by guiderolls 19, and further sizing rolls 22 and 24 press against the opposite sides of belts 12 and 11, respectively, throughout the cooling and solidifying region and serve to maintain the selected, predetermined distance between belts 11 and 12, depending upon the thickness desired in the resulting cast strip 25 which is continuously removed at the other end of the machine at driving pulleys 15 and 18, as indicated.

the rough, adherent iron oxide coating deposited on the belts so that no bare metal surface of belts 11 and 12 is exposed to direct contact with the molten metal. .The

rough surface of the iron oxide coating on belts 11 and 12 provides an excellent insulative coating since the cavities and depressions on the surface of and within the iron oxide coating serve to trap gas, such as air, therein when in contact with and covered by molten or solidified metal. Thethus-entrapped gas possesses excellent insulative properties and further protects'the iron oxide coating from direct contact with the hot molten metal.

Referring now to PEG. 2 of the drawings, there is illustrated therein in a schematic, cross-sectional view, an endless metal belt coated on one side or surface only with a rough, adherent iron oxide coating 31 as prepared and deposited thereon in accordance with this .uvention.

Exemplary of the practice of this invention satisfactory, rolling quality slab aluminum alloy, actually Alcan Alloy 6107 aluminum having a nominal magnesium content of about 0.80%, was 'cast in a continuous casting oper- Desiration employing iron oxidecoated mild steel belts having a thickness of. about 0.05 inch. It was observed that when these iron oxide coated belts were employed in the continuous metal casting operation, a minimum of thermal distortion occurred in the belts, thereby permitting a life expectancy of the belts in excess of 8000 .feet of alloy slab or about 200,000 pounds of alloy slab having cross-sectional dimensions of A" x' 28".

As will be apparent to those skilled in the art in the light of the accompanying disclosure, many modifications, alterations and substitutions are possible in the practice of this invention without departing from the spirit or scope thereof.

Iclairn:

Ina continuous aluminum casting apparatus including endless belt rollers, and means for. the introduction of a molten aluminum body, the improvement in combination therewith which comprises a flexible endless steel belt for directly restraining said molten aluminum body having an inner structural layer carried by said rollers and an outer layer for contact with said molten aluminum body, the inner structural layer of said belt.

comprising a steel body,'and the outerlayer of said belt comprising red iron oxide having a high degree of self-cohesion and having a relatively uniform thickness References Cited by the Examiner UNITED STATES PATENTS 1,965,340 7/34 Heinicke 1486.35 XR 2,728,696 12/55 Singer 148-6 .14 XR 2,904,860 9/59 Hazelett 2257.4 3,085,03 4/63 Croessant et al. 148-635 FOREIGN PATENTS 475,228 I 7/51 Canada.

509,752 2/55 Canada.

465,509 8/35 GreatBritain.

WILLIAM J. STEPHENSON, Primary Examiner.

ROBERT F. WHITE, WINSTON A. DOUGLASS,

Examiners. 

